A number of insects infest human habitations, and methods to eradicate one type of insect are often effective against other unwanted insects. For instance roach and ant treatments may eradicate orthopterous species such as crickets, various types of flies, and other species. For parsimony's sake roaches and ants are discussed here as representative invasive species since they are among the most prevalent. Of the 4,000 species of roaches, 30 are associated with human habitations. The most invasive of these include the American cockroach (ca. 30 mm, 1.2 in.); German cockroach (ca. 15 mm, 0.5 in.), Asian cockroach (15 mm), and Oriental cockroach (25 mm, 1 in.). Most cockroach species adapt readily to a variety of environments, but they thrive in tropical and subtropical climates, and pest species especially prefer the warm conditions inside buildings. Ant infestations (order Hymenoptera) are also problematic; the worst invasive species include the pavement ant, yellow crazy ant, sugar ants, Pharaoh ant, carpenter ant, Argentine ant, odorous house ants, red imported fire ant and European fire ant.
The natural behaviors of these insects exacerbate infestations. Both roaches and ants leave chemical trails (by feces in the case of cockroaches) that other individuals of their same respective kind use to find food or water. Such trails also announce roach hiding places. Thus group behavior can be precipitated by a single individual's activity. Airborne pheromones likewise facilitate swarming and mating. Roaches and ants both reorganize their colonies quickly to adjust to changes in shelter conditions. However ants are diurnal, whereas for the most part roaches (with the exception of Asian cockroaches) are nocturnal and flee from light.
At a minimum, infestations are a nuisance, but they can also cause damage and illness. In a home, cockroaches and ants commonly feed on food, even pet food, as well as garbage, and they leave an offensive odor. See, e.g. R. J. Brenner, et al., Infestations in Med., 4(8):349-355 (1987). Roaches are omnivorous, so they can damage personal property including wool, leather, paper, and the paste in book bindings. They are also a health hazard. Roach body surfaces passively transport human infectious diseases. C. Rivault, et al., Epidemiol. Infect., 110(2):317-25 (April 1993); R. M. Elgderi et al., Ann. Trop. Med. Parasitol., 100(1):55-62 (2006). Infestations also trigger allergic reactions in humans. H. S. Bernton and H. Brown. J. Allergy, 35:506-513 (1964); B. Kutrup, Turk. J. Zool., 27:73-77 (2003). These allergens have been linked to asthma. B. Kang et al., J. Allergy Clin. Immunol., 63(2):80-6 (1979).
Exterminating these pests can be daunting because their colonies are prolific and hardy, often with exponential growth. Cockroaches live for up to two years, depending on the species, and females commonly produce 300-400 eggs each, in some cases requiring only one impregnation for life or none at all. The nymphs hatch and reach adulthood in four months or less. Some species can go without air for 45 minutes or reduce their heart rate. American cockroaches can live three months without food and a month without water. And roaches can survive occasional freezing temperatures. Like many other insects, roaches are up to 15 times as radiation-resistant as humans partly because they are only specially genetically vulnerable during cell division at molting time. Consequently the easiest way to deal with infestations is to prevent them.
Physical preventative measures include storing all food in sealed containers, sealing garbage in tightly lidded cans, cleaning the kitchen frequently, and vacuuming regularly. Water taps and lines must be kept in good repair and insulated because drips even from condensation provide a water source for roach or ant colonies. And entry points, such as under baseboards, in between kitchen cabinets, and at pipes, doors and windows, must be blocked with steel wool or copper mesh and cement, putty or caulk. Unfortunately air-tight houses present their own problems, such as the retention of unwanted radium or mercury vapors that emanate from the ground and remain bound especially to particles in cigarette smoke that cling to walls. And if even one pregnant female roach enters the building such as by scurrying unnoticed through an open door, physical preventative measures may not exterminate the colony that forms as a result.
A severe alternative requires evacuating the premises for a few days while it is fogged by fumes from burning sulfur: the effects are said to last several years. However this not only displaces the human occupants, but also exposes walls and furnishings to the corrosive fumes, and requires precautions to avoid user asphyxiation, e.g., a gas mask.
Natural extermination methods are more attractive, but have had limited use. Cockroaches and ants have natural enemies including parasites and predators such as wasps and centipedes. Wasps are effective; those in the family Evaniidae attack roach egg cases, and those in the family Ampulicidae prey on adult and nymphal cockroaches (e.g., Ampulex compressa). The house centipede is probably the most effective control agent. Yet many homeowners do not want either type of predator in the house. Bunches of leaves of the Pandan plant (Pandanus amaryllifolius Roxb.) are said to be used as a roach repellant in Asian taxis. But their active compounds are volatile (thus less effective in dried leaves), and necessary concentrations may be hard to sustain in open air spaces.
In America the so-called Las Vegas trap has become popular, and also uses a natural approach. In this method coffee grounds or other food is placed with or without moisture into a slick glass open jar. The jar may be taped on the outside to facilitate climbing by the roaches, and greased inside with petroleum jelly to hinder escape up the sides, or the jar may simply be stood next to a wall. Such traps are useful for killing individual insects, sometimes a large number of them, however they do not tend to wipe out the entire colony nor do they kill live eggs that remain in the nest.
Partly because of these shortcomings of traps, professional exterminators prefer to use baits instead. The baits are toxic formulations that contain an attractant and are generally applied indoors. The baits are particularly effective because cockroaches and ants are cannibalistic, eating the corpses of downed individuals, cockroaches also eat their own feces, so the toxin is recycled and it kills additional individuals in each iteration of consumption by the colony. Baits are currently sold mostly in gel forms, under several brand names, including ADVANCE®, AVERT®, ADVION®, COMBAT®, DRAX®, INTICE®, SIEGE®, and MAXFORCE®, among others.
A typical bait gel's active ingredient is commonly hydramethylnon, fipronil, deltamethrin or pyrethrin. Baits that kill eggs can also reduce populations, but the results are slower. To convince end-users that the product works, even roach baits that employ the natural insect juvenile hormone—which is slow-acting—often include a “knock-down” additive poison to kill roaches on contact. Boric acid powder as well as borax are also toxic to cockroaches. Among the chemical alternatives, the boric compounds are the most natural, and are also relatively non-toxic to pets that might ingest them. The sharpness of fine boric acid crystals is thought to abrade cuticle and joints in the roach's exoskeleton, and boric acid also dehydrates. Boric acid is also used to exterminate flies such as fruit flies. www.bio.umass.edu/biology/kunkcl/cockroach_faq.html#U8.
For the more toxic compositions several manufacturers sequester the material in a bait station to prevent consumption by children or household pets, but this is not the only reason. Baits and sprayed insecticides have opposite mechanisms—a bait is a “trojan horse” whereas an insecticide kills on contact and repels—thus baits are often placed at a significant distance from any sprayed insecticide. Also, boric acid is washed away by water, thus direct use of the powder is limited to sites that are seldom wetted.
An illustrative roach bait is taught in U.S. Pat. No. 6,007,832, issued to Stapleton. The bait contains 15 to 35% boric acid, supplemented by one or more attractants and an additive selected from ascorbic acid, lipids, monosaccharides, gums, silica, and pectin. The attractant particularly disclosed was a dough of milk, onion, flour and sugar. The bait was disclosed to have a substantially paste or gelatinous consistency initially, adhering to surfaces, and within hours of application was said to dry as hard as plaster.
Master Roach Kill™, which was granted EPA pesticide registration no. 55540-20205 on a 1986 application by James Mullis, also contained milk, onion, flour, sugar and boric acid, but without the additives. It was marketed in the form of small balls; these also adhered to surfaces when fresh but hardened shortly after placement.
PCT Application No. WO 2007/010095 filed by Oy Finnpesticides Ltd. discloses a roach and ant bait composition of milk powder, onion, flour, sugar and boric acid, additionally containing water as well as 10-14 wt % potassium sorbate and 2-4 wt % each of alum, glycerine and citric acid.
Because of boric acid's effectiveness, natural source, environmental friendliness and low toxicity to humans and pets, it remains a preferred method to treat infestations of ants, roaches and other insects. However the presentation methods required for dry baits have fallen out of favor. For distribution the pesticide application industry prefers syringes, squeeze tubes, and caulk gun tubes; hard bait particles are not very compatible with this equipment. Moreover baits that remain soft and moist are more attractive to insects than are dry or hardened baits. Yet gels can often leave a sticky or unwanted residue after drying. Thus there is a continued need for improved formulations and processes that can provide the required physical and biological properties for baits.